Cathode ray tubes



R. R. PEARCE cA'monE RAY Aug. 4, 1959 TUBES 2 Sheets-Sheet 1 Fild Jan. 127, 1956 S D: mvm/m Aug- 4, 1959 V R. R. PEARCE 2,898,491

` CATHODE RAY TUBES Filed Jan'.v v27; 195e 2 sheets-sheet z Lili States Pate-m v Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application January 27, 1956, Serial No. '561,827

Claims priority, application Great Britain February 12, 1955 12 Claims. (Cl. 313-70) The present invention relates to cathode ray tubes having a plurality of electron gun structures.

Cathode ray tubes having a plurality of gun structures so as'fto produce a plurality of electron beams have been proposed for various purposes, one importa-nt application for such tubes being for the reception of television pic? AturesV in colour. The various individual guns are each modulated with information signals concerning Ya particular colour and the guns are grouped so that. the individual beams are directed on to a common luminescent target having an array or pattern of phosphor particles'ldisposed thereon which on being struck by electrons `produce diferent colouredr light ile." red, vgreen and blue. The manner of grouping the electron guns will depend to a large extent on the phosphor pattern on the: target and at present two such arrangements are'well known. In one arrangement three guns are providedv in the neck of the tube land positioned symmetrically around the. neck axis and each slightly inclined thereto, so that 4the three electron beams arriving at the target or at a shadow 2 the beams emerging from said guns can be positioned closer to each other than would otherwise be possible with similar guns all arranged at the sameraxial position in said neck. Y

In order that the invention may be clearly understood and readily carried `into effect, embodiments of same will now be more fully described with reference to ligures of the accompanying drawings, in which:

Figure 1Y shows one arrangement for a group of three guns housed in the neck portion of a cathode'ray tube envelope, said guns facing a luminescent target electrode,

Figure 2 shows an alternative arrangement of guns having modied gun electrodes, and

Figure 3 illustratesra gun arrangement similar to that of Figure l but with a moditedgun structure. Y

Referring to Figure 1 there is shown three electron guns each comprising a thermionic cathode 1, an apertured grid electrode 2, an apertured disc vanode electrode 3 having attached thereto an annular extension 4, a second anode electrode 5 of tubular form and a third anode electrode' also of tubular form. ln operation of the tube the signal potentials are applied to each gun between the cathode 1 and modulating electrode 2 Aand the anode 3 maintained at a suitable potential with respect to the cathode 1. A positive potential with respect to the cathode 1 is applied to the second anodefS and a much higher positive potential to the third anode `6 so that mask provided adjacent thereto, form the apices of small 'equilatera'l triangles. In a second arrangement, the threeV electron guns are mounted side by side in one plane, the

centre gun having its axis coinciding with the axis ofthe A neck of the tube and the outer guns each. being inclined 'towards the tube axis so thatV three focussedV spots'sare `formed at or near the phosphor target, in line and at a small distance apart. Y

Withsuch arrangements the practice `is to construct,

each f the guns with independent electrostatic .focussing `means `for each of the beams in order to overcome the vdiiculties, which would arise with a commonmagnetic or electrostatic focussing means for such widely separated -and inclined beams. Thediameter of the neck ofthe tube, the angle of convergence of the beam .and the, over- 'all length of the tube will impose limitations onrthe dilameters of the lenses Awhich can be employed'.,for the `-lthree guns, particularly in the simple side by` side arrangement, n'which results in anV unfavourable ratio of lens to` beam?,` diameter and consequent aberrationV in V,the focus-especially in the highlights of ,the picture., The

--beamrdiameter is usually set by electron'optical conlsiderations in the gun design and it issdesirable toin ici-ease the diameters of thellens electrode as. much as possible. "f

- It is therefore an object of the present .invention to provide an improved arrangementV for'providing a; plu- -ralityy of electron gun structuresin Va cathode 4ray tube "'wherebyn the lens to A beam ratio ofi the. individual .guns

be` im1:r'o`ved.VV

" Accordinglythe invention c o'mprisesa cathode ray tube having Yafplur'ality of independent guns" arranged 'as a,

fgroup the Atubular` neck portionof the envelope'of "said tube, wherein one of'said displaced sofas to ,occupy a different positionralong the length ofk `said normal-to the plane of the drawing. It will be observed that the anodes 5 and 6 each have a larger diameter at the position'll where the Velectron lens is formed and it is this diameter, termed lensrdiameter, which determines 'the-'closeness' withVwhich the electron guns-can be disposed as a group in the glass neck 12 of thercathode ray tube.v A wall anode 13 is provided extending between the ends of said guns and the target. Y

v For electron optical reasons the lens diameter should Y be as large as practical and further it is desirable, particularly with cathode ray tubes employed for colour television that the focussed beam spots should formfan accurate closely spaced group at the position ofthe In the example illustrated the three electron guns are shown disposed in a single plane with theraxis'of the `centre gun coincident with the axis of the cylinder V12.

However the centre gun is arrangedat a diiferent axial position along the neckrlZ- compared with the out`er`guns of the group. In order Vto provide a suitable convergence of the beams of the` outer guns on to the target these guns Yare arranged with their respective'axes inclined Ytowards the axis of the neck 12, and to prevent interaction betweenthe beams due to the positioning of the centre gun,

the vanodes 6 of the outer guns are each provided with a tubular extension 14Yso that the beam Vexit aperturesY of lallthre'e Vguns are at approximately the sameaxialiposition. The provision of-thean'nul'a'r extensions flon the Aanode 3 will serve-to screen the modulatorfzandahode i5 'from any disturbing eld conditions which may be set Vrup due to the proximity of high potential Yelectrodes of `adjacent guns, particularly, the centre'gun inrespect to the fields of the anodesy of the other two To'- ther minimise `any possibility of distortion'iofthe lens gneckfthanfanotheror other. gunsg'of; group whereby 2 iieldsdue'to the proximity of the other 'guns,th *space 11 between the anode electrodes and 6 may be screened in any suitable manner such as illustrated in'Figures 2 and 3. In these figures parts similar to those of Figure 1 are given the same reference numerals.v Referring to Figure 2 it will be seen that the larger' end of each of the anodes 6 is of slightly smaller Vdiameter than the diameter of the adjacent portions of the anodes 5 so that the ends of the anordes 6 project ifor a short'distance into the `anodes 5 thereby screening the lens 'space between these electrodes from the fields of adjacent guns. v

A slightly different arrangement for screening the lens spaces of the guns is shown in Figure`3 yand comprises annular screen members 15 surrounding the lens gap betweenanodes 5 and 6 for each gun. These members 1 5 may b@ connected electrically either to anode 5 or to anode 6. Y

The amount by which the centre gunv can be displaced with respect to the other guns will depend in the `above arrangements on the angle of convergence required in -the beams, the separation of the gun axes at a given distance from the target, the lens diameters, the diameter, and total length of the neck.

A further advantage which arises from the use of a series of guns grouped according to the invention is that individual corrections of the angle of convergence of the outer lguns in a side by side arrangement or of all guns in a symmetrical arrangement, by magnetic means to take account of inaccuracies in assembly is simplilied, in that magnetic elds local to any particular gun can beset up so as to have little or no eifect on the beams from the @ther gurls- Various modications may be made in the manner of staggering the various guns of the group, for example, as shown in Figure 2, the outer guns of the arrangement bove described may be setrforward of the centre gun, and it will of course be understood that guns having a different electrode arrangement such as those illustrated in Figures 1 and 3 may also be employed and positioned in the manner shown in Figure 2.

" It will be appreciated that since each of the gunsl is in operation, independent of the other guns, adjustments to ifect a change in the rfocal length of the lenses to compensate for their different positions in the tube may be effected electrically by slightly changing the Voltage ratio applied to the anodes Strand 6, or if preferred the length and/or diameter dimensions of the anodes S oi the two outer guns may be made different from the dimensions of anode 5 of the centre gun.

Although the invention has been vdescribed applied to cathode ray receiving tubes it is also applicable to transinitting tubes and generally to cathode ray tubes irrespective of purpose where a plurality of guns are required with their respective beams -focussed into a group of spaced spots on to a suitable target electrode.

What I claim is: Y

1. A cathode ray tube having an envelope including a `tubular neck, a target within said envelope lfacing said neckand a plurality of electron guns within said neck facing said target, said guns each having means for producing an independent electron beam and electrodes prod viding an electrostatic lens for focussing its electron beam .at said target so that the focused beams of said plurality closer to each other than would otherwise be possible with a similar plurality of guns having electrodes providing the same lens diameter arranged with said electrostatic lenses at the same axial position in said neck.

2. A cathode ray tube according to claim 1 in which one of said guns is provided with electrodes spaced apart and forming therebetween the electrostatic lens of said gun wherein means is provided surrounding the position at which said lens yiield is formed between said spaced electrodes to substantially shield said lens from the field of an electrode of an adjacent gun.

3. A cathode ray tube according to claim 1 in which one of said guns includes two spaced tubular electrodes forming the electrostatic lens of said gun, wherein an electrically conducting member is provided surrounding the space between said tubular electrodes said member being electrically connected to one of said tubula-r electrodes to substantially shield said lens from the eld of an electrode of an adjacent gun.

4. A .cathode ray tube according to claim 1 wherein the electrostatic lens of one of said guns is produced by a pair of tubular electrodes of dilierent cross sectional dimensions, the electrode of smaller cross section projecting into the electrode of larger cross section to an extent such as to substantially shield the electrostatic lens field formed between said electrodes from the iield of an electrode of an adjacent gun.

5. A cathode ray tube according tovclaim l wherein the beam exit apertures of each of said guns is arranged at substantially the same axial position along the neck of said tube.

6. A cathode ray tube according to claim l wherein one of said plurality of guns is arranged with its axis substantially coincident with the axis of said tubular 4neck and another of said guns is arranged with its axis tilted toward the axis of said rst mentioned gun.

7. A cathode ray tube according to claim 1 wherein a group of three electron guns are provided, and said target comprises a luminescent screen providing three different colours the means for producing said dilerent colours being arranged in a pattern of triplet groups over said target, the electron beams from said electron guns having such an angle of convergence that the beam from of guns arrive at said target as a group of spots which are spaced from each other, the electrodes forming the electrostatic lens of each of said guns being of substantially the same cross-sectional dimensions for each gun at said lens position, one of said guns being provided with `an electrode portion which is oi a smaller cross-sectional dimension than the electrodes at said lens position and another of said guns arranged with its electrode at its lens position disposed adjacent the electrode loi srnaller cross-sectional dimension of said rst mentioned lgun with said electrostatic lenses of `said first and second. guns displaced so as to occupy diiierent axial positions along the length of said neck and such that said guns are positioned each of said guns .will impinge on adifrerent colour producing'means on arriving at a triplet group at said target. 8. A cathode ray tube having an envelope including a -tubular neckQa target within said envelope facing said neck and a group of three electron guns within said neck facing said target said guns each having means for producing an independent electron beam and electrodes of substantially the same cross-sectional dimensions for forming van electrostatic lens for focusing said beam at said target,said electron guns being mounted side by side in a common plane with the axes of the two outer guns converging in the direction towards said target one of said gunsbeing provided with an electrode portion which VVis of a smaller cross-sectional dimension than the electrodes at .said lens position and one of said guns being displaced so as to occupy a different axial position along the length of said neck with the electrode at its lens position disposed adjacent the electrode of smaller dimension of said other gun such that said three guns can be positioned closer to each other for a prescribed angle of 'convergence of said beams than would otherwise be pos- -sible with three similar guns mounted in a common plane `and all arranged at the same axial position in said neck. f 19. A cathode ray tube according to claim 8 wherein the axis of the center gun substantially coincides with the -axis of said neck withrsaid outer two guns having their axes tiltedtowards the axis o f said center gun the electrostatic lensof said center gun occupying a different axial position alongthe length of the neck of said tube than i .the electrostatic. lens of said outer guns.

.410. A cathode raytubeaccording to claim 8 wherein sadvta'rget cmprises'a'luminescent screen composed of 5 a repeating sequence of groups of line phosphors each group providing three diierent colours, said guns being arranged such that the angle of convergence of said beams is such that each individual beam strikes a diierent colour phosphor of a group.

1l. A cathode ray tube according to claim 8 wherein the center gun of said three guns is of greater axial length than the outer two guns said center gun being disposed with its axis substantially coincident with the axis of the tubular neck with said outer two guns disposed With their axes tilted towards the axis of said center gun, the exit aperture of each of lsaid guns being arranged at substantially the same axial position along the neck of said tube.

12. A cathode ray tube according to claim 8 wherein the outer guns of said three guns are of greater axial length than the center gun, said center gun being disposed with its axis substantially coincident with the axis of the 6 tubular neck with said outer two guns disposed with their axes tilted towards the axis of said center gun, the exit aperture of each of said guns being arranged at substantially the same axial position along the neck of said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,459,790 Busignies Jan. 25, 1949 2,563,500 Snyder Aug. 7, 1951 2,593,261 Buchanan Apr. 15, 1952 2,674,704 Weimer Apr. 6, 1954 2,761,089 Haei Aug. 28, 1956 FOREIGN PATENTS 866,065 France Mar. 31, 1941 

